Earth Structure Notes

Oceanic Crust:
- Floats on the Asthenosphere.
- Ferro-magnesium silicates.
- Denser rocks.
- High in iron, calcium, and magnesium.
- Darker colored rocks.
- Less silica (SiO_2).
Continental Crust:
- Floats on the Asthenosphere.
- Non-ferro magnesium silicates.
- Lighter colored rocks.
- More silica (SiO_2).
- Less dense rocks.
- Large amount of potassium (K) and aluminum (Al), some sodium (Na).

Lithosphere:
- Crust and uppermost solid mantle.
Asthenosphere:
- Lower part of the upper mantle and middle mantle.
- Hot plastic state (capable of flow).
Mesosphere:
- Lower mantle.

Mohorovicic Discontinuity (Moho):
- Transition from the mantle to the crust.
Gutenberg Discontinuity:
- Transition from the outer core to the lower mantle.
"D" Double Prime Layer:
- Also represents the transition from the outer core to the lower mantle, a region known for complex interactions between the core and mantle.
Conrad Discontinuity:
- Boundary within the continental crust (separates SIAL and SIMA).
Repetti Discontinuity:
- Boundary within the mantle, separating the upper and lower mantle.
Lehmann Discontinuity:
- Boundary between the Earth's inner and outer core.

SIAL:
- Refers to the upper layer of the continental crust, rich in silicon and aluminum.
SIMA:
- Refers to the lower layer of the crust (both oceanic and continental), rich in silicon and magnesium.
NIFE:
- Refers to the Earth's core, which is primarily composed of nickel and iron.

P-waves: Can travel through solid and liquid.
S-waves: Cannot travel through liquid; creates a shadow zone.
No direct S-waves observed beyond 103° from the epicenter due to the liquid outer core blocking their propagation.
P-waves are refracted (bent) as they pass through different layers within the Earth, indicating changes in density and composition.